In recent years, research in logic circuits employing Josephson tunneling-junction devices (hereinbelow termed "Josephson devices") has been vigorously conducted. In order to drive the logic circuit, a rectifying circuit for obtaining a stable D.C. voltage of low magnitude on the order of several mV from a commerical A.C. power source has been desired.
In one type of rectifying circuit, a direct current is obtained by passing an alternating current from a commerical A.C. power source through a transformer to bring it to a predetermined voltage, which voltage is then subjected to full-wave or half-wave rectification by means of a rectifying device, such as a diode, and is filtered using a coil, a capacitor or the like. The prior art circuit, however, has the disadvantage that it is difficult to obtain a stable D.C. voltage of low magnitude on the order of several mV because of the thermal noise produced by the rectifying device, such as a diode, constituting this circuit.
By way of example, the thermal noise at room temperature of 300.degree. K. is as great as approximately several tens of millivolts, and therefore, a D.C. voltage on the order of several mV cannot be stably obtained with use of such a rectifying device at room temperature.
In an effort to eliminate the influence of the thermal noise on the system, it has also been considered to rectify the A.C. voltage by means of a diode which is maintained at the extremely low temperature of 4.degree. K. at which the Josephson device operates. At such an extremely low temperature, however, the diffusion coefficient of a semiconductor becomes substantially zero, and the semiconductor diode does not operate, so that rectification is impossible.